1. Field of the Invention
This invention relates to apparatus for cooling electronic circuit modules and particularly to cooling such modules of the type which are mounted in racks.
2. Discussion of the Prior Art
Commercial electronic equipment such as processors and controllers is commonly made by mounting modules which include the printed wire boards (also known as printed circuit boards or circuit cards) that perform the electronic functions of the equipment in frames, known as "racks". The modules are usually mounted side-by-side in the racks vertically or horizontally and are slidable in "slots" defined by edge guides of the rack. Several rows or columns of modules may be provided in a single rack, and several racks may be mounted in a self-contained enclosure. One board, known as a "back plane", at the rear of the rack has connectors mounted on it to electrically mate with corresponding connectors on the modules as they are slid into the rack and makes interconnections between the modules and to controls and I/O interfaces mounted on the exterior of the enclosure.
As is well known, many electronic components generate considerable heat, and will self-destruct unless they are properly cooled. Thus, it is often necessary to provide a certain minimum air flow rate over the components on a printed wire board to insure proper operation of the equipment.
Cooling is usually provided to rack mounted electronic circuit modules by providing fans in the enclosure to force air through the racks in the direction of the boards, i.e. a vertical air flow for vertically mounted boards and a horizontal air flow for horizontal boards. However, cooling problems can arise when less than all the slots in a row, for vertically mounted boards, or less than all the slots in a column, for horizontally mounted boards, are filled. In those cases, the cooling air will flow through the open spaces rather than over the electronic components where there is more resistance to flow.
Another problem with cooling arises when boards of different sizes are used in the same rack. In that case, a board which is too small to fill a slot by itself is mounted in an adaptor plate which, in combination with the board, is sized and shaped to fill the slot. Typical cooling of boards so mounted results in most of the cooling air flowing around the board, i.e. over the surfaces of the adaptor plate, rather than over the components mounted on the board.